STRUCTURAL AND STEREOCHEMICAL STUDIES OF POTENT INHIBITORS OF GLUCOSYLCERAMIDE SYNTHASE AND TUMOR-CELL GROWTH

Analogs and homologs of PDMP were synthesized, based on its structure 1-phenyl-2-decanoylamino-3-morpholino-1-propanol). This compound had p reviously been found ro block the synthesis of GlcCer (glucosylceramid e). Increasing the acyl chain length from 10 to 16 carbon atoms greatl y enhanced the efficacy of the enzyme inhibitor, as did the use of a l ess polar cyclic amine, especially a pyrrolidine instead of a morpholi ne ring. Replacement of the phenyl ring by a chain corresponding to sp hingosine also yielded a strongly inhibitory material. By using a chir al synthetic route, we showed that the isomers active against GlcCer s ynthase had the R,R-(D-threo)-configuration. However, strong inhibitio n of the growth of human cancer cells in plastico was produced by both the three and erythro racemic compounds, showing involvement of an ad ditional factor (beyond simple depletion of cell glycosphingolipids by blockage of GlcCer synthesis). The growth arresting effects could be correlated with increases in cellular ceramide and diglyceride levels. The aliphatic pyrrolidino compound was strongly inhibitory toward the glucosyltransferase and produced almost complete depletion of glycoli pids, but did not inhibit growth or cause an accumulation of ceramide. Attempts were made to see whether the differences in growth effects c ould be attributed to the influence of the inhibitors on related enzym es (ceramide and sphingomyelin synthase and ceramidase and sphingomyel inase). While some stimulation of enzyme activity was noted, particula rly at high inhibitor concentrations (50 mu M), these findings did not explain the differing effects of the different inhibitors. The best i nhibitors of GlcCer synthase compared favorably in efficacy with some cancer chemotherapeutic drugs in current use when tested with a batter y of human cancer cells.